Over the last 20 years, brake disks have been made of carbon because it has characteristics at the high temperatures encountered while brakes are in operation that are much better than the characteristics of the metals that used to be used for brake disks.
At their periphery, brake disks have open slots with faces that are parallel or inclined, each slot receiving an axial bar (of rectangular or trapezium-shaped section), braking torque then being transmitted via the lateral faces of the slots and the axial bars. Between them, the slots define circumferential segments which are totally or partially covered by curved channel-section caps open towards the body of the disk, which caps are held in place by through bolts or rivets extending parallel to the axis of the disk. Such a disposition can equally well be provided both for rotor disks that transmit braking torque to the wheel via the corresponding axial bars mounted inside the wheel (slots on the outer periphery of the disk), and for stator disks (slotted on the inside periphery of the disk, receiving bars or splines on the brake torque tube).
To prevent the bars from coming directly into contact with the carbon, the lateral faces of the slots that serve to transmit braking torque are protected by a thickness of metal which either forms a portion of the caps, or else is constituted by an insert.
Numerous solutions have already been proposed for providing such protection.
Particular mention may be made of the following documents: U.S. Pat. No. 3,924,740, U.S. Pat. No. 3,972,395, U.S. Pat. No. 4,007,814, and U.S. Pat. No. 4,083,434, which describe configurations in which each slot is bridged circumferentially by a reinforcing cap having a setback whose lateral walls bear against the lateral faces of the slot in the carbon rotor disk. In a variant, the Applicant has proposed a cap or "rider" overlying each circumferential segment of the carbon disk, said cap having two parallel end walls protecting the lateral faces of the slots (U.S. Pat. No. 4,890,700), that solution having the advantage of facilitating installation of the caps and of providing the circumferential segments with good protection against oxidation.
For solutions of the type having keyway members or "inserts", mention may be made of document U.S. Pat. No. 3,891,066 which describes trapezium-shaped keyway members which are held axially in position by two annular rings disposed on either side of the outer periphery of the disk, and which are held radially in place by rivets passing through the two rings. It should be observed that the peripheral edge is then bare, and thus poorly protected against oxidation. Document U.S. Pat. No. 4,784,246 describes hood-shaped half-inserts each covering one lateral face of a slot together with the surrounding zone of the disk, with radial support being provided by snap-fastening a curved tab in a notch. An analogous approach is to be found in document FR-A-2 546 250. Mention may also be made of document U.S. Pat. No. 5,273,140 which describes annular inserts having peripheral grooves. In those various solutions, the non-rubbing portions of the carbon disk are poorly protected against corrosion.
Finally, it is of interest to mention document U.S. Pat. No. 4,465,165 which illustrates a reinforcing device constituted, for each slot of the disk, both by means of a U-shaped insert whose outside profile corresponds to the profile of the slot, having a central limb that bears against the bottom of the slot, and two lateral limbs whose inside faces are disposed to face the lateral faces of the corresponding coupling bar, and by means of two channel-section caps each covering a portion of a respective circumferential segment adjacent to the slot, and being fixed to the corresponding segments by rivets. It should be observed that the inside faces of each of the U-shaped inserts are projecting relative to the free end edges of two adjacent channel-section caps so that contact with the lateral faces of the corresponding coupling bar takes place exclusively via the inside faces of the U-shaped insert.
Finally, it may be observed that each of the two above approaches has its own advantages and drawbacks when it comes to transmitting braking torque, to staying in place during operation, and to providing mechanical and/or anti-oxidation protection for the non-rubbing portions of a carbon disk.